1. Field of the Invention
The present invention relates to an axle bearing unit with a rotational speed sensor for an automobile used to maintain an axle for an automobile wheel of a commercial vehicle or a small truck or the like in a freely rotatable manner, and to sense the rotational speed of the axle.
2. Description of the Prior Art
A rear axle of a normal front-engines, rear-wheel-drive vehicle (often referred to as FR vehicle) is provided to extend through an axle housing or axle tube which is maintained via a spring on the underfloor surface of the chassis, and both ends of the rear axle are maintained in a freely rotatable manner by means of single-row rolling bearings such as ball bearings, tapered roller bearings, cylindrical roller bearings, or the like. The bearing for supporting one end of the rear axle is placed on the side closer to the differential gear, and the bearing for supporting the other end of the rear axle is on the side closer to the wheel.
The support structure shown in FIG. 7, for example, is disclosed in FIG. 4 of Japanese Patent First Publication No. H1-288619 as a conventional structure in which a rear axle 5 on an FR vehicle is supported in a freely rotatable manner with respect to an axle housing or tube by bearing 3. It will be noted that the bearing 3 is arranged together with a bearing housing 2 and a sealing member 29 etc. in one assembly. An axle housing or tube 1 is supported on the underfloor surface of an automobile through a leaf spring or the like and connected at one and to a casing of a differential gear (not shown), while the other end of the axle tube is provided with an open end section 1a on the side closer to the wheel (not shown) to allow connection to the bearing assembly as mentioned above.
In the bearing assembly provided on the wheel side, the cylindrical bearing housing 2 is secured by welding to the open end section 1a of the axle housing or tube 1. An outer ring 4 which forms part of the ball bearing 3 is fitted into the cylindrical bearing housing 2. The axle 5 is inserted through the above-mentioned axle tube 1 and has one end connected to the above-mentioned differential gear. An inner ring 6, which also forms part of the ball bearing 3, is fitted around at the other end, closer to the wheel, of the axle 5. A plurality of balls 9 is mounted between an outer ring raceway 7 on the inner peripheral surface of the outer ring 4 and an inner ring raceway 8 on the outer peripheral surf ace of the inner ring 6, so that the axle 5 rotates freely on the inside of the axle housing or tube 1.
One and of the outer ring 4 (the left end in FIG. 7) is abutted against a stepped section 10 formed on the inner peripheral surface of the bearing housing 2, and the other end of the outer ring 4 (the right end in FIG. 7) is abutted against a retaining cover 12 via a backing plate 11 (a member which acts as a baseplate for a drum brake).
The retaining cover 12 and the bearing housing 2 are connected by means of a bolt 13 and a nut 14 to prevent the outer ring 4 from falling out of the bearing housing 2. One end of the inner ring 6 (the right end in FIG. 7) is abutted against a stepped section 15 formed on the outer peripheral surface of the end, closer to the wheel, of the axle 5, and the other end of the inner ring 6 (the left end in FIG. 7) is abutted against the end of a securing ring 16, which is fitted around the axle 5, thus positioning the inner ring 6.
Japanese Patent First Patent Publication No. H1-288619 discloses, in FIG. 3, an integral structure of a single-row ball bearing with a mounting flange to improve the prior art structure as in FIG. 7.
Disclosed in Japanese Patent First Publication No. H2-60802 and Japanese Utility Model First Publication No. H2-83102 are a similar structure in that the outer ring is integrally formed with a mounting flange in a single-row ball bearing structure.
It should be noted, however, that no speed sensor is taken into consideration and combined with the bearing in these publications.
Accordingly, the bearing assembly on the wheel side as mentioned above with reference to FIG. 7 is conventionally modified as shown in FIG. 8 in the case where the rotational speed of the axle 5 is detected to control an antilock brake system (ABS) and a traction control system (TCS).
In FIG. 8, a pulser ring 17 which has its outer peripheral surface formed in a gear teeth shape is formed around the axle 5 and interposed axially between the inner ring 6 and the securing ring 16 to rotate with the axle 5. Also, at one end of the bearing housing 2, an installation hole 18 is formed at a position facing the outer peripheral surface of the pulser ring 17.
A sensor 19 with a support arm 20 is inserted into the installation hole 18 from the outside of the bearing housing 2. The tip of the sensor 19 faces the outer peripheral surface of the pulser ring 17. In addition, the support arm 20 of the sensor 19 is secured to the outer peripheral surface of the bearing housing 2 by a stud 21 screwed into a nut 22.
When the pulser ring 17 secured to the axle 5 rotates during the operation of the vehicle, the distance between the outer peripheral surface of the pulser ring 17 and the tip of the sensor 19 changes so that the output e.g. the amount of magnetic flux of the sensor 19 changes. Because the frequency of this change is proportional to the rotational speed of the axle 5, the ASS and the TCS can be controlled by enputting an output signal from the sensor 19 to a controller (omitted from the drawings).
The conventional assembly shown in FIG. 8 has a large number of structural parts, therefore the management of the parts and the assembly operation are complicated, resulting in high manufacturing costs. In addition, because the weight, in particular, the weight supported by the springs, is increased, the ability of the wheels to follow irregularities in the road surface is worsened, which is believed to cause the comfort sensation of the ride to worsen. Further, even an increase in weight, although small, causes an increase in fuel costs.
On the other hand, for example, structures for unitizing an axle bearing for supporting a wheel axle, a sensor and a pulser ring for sensing rotational speed are disclosed in Japanese Utility Model First Publication Nos. S62-170363 and H3-30864; U.S. Pat. Publication Nos. 4,778,286, 4,864,231, 4,960,333, and 5,018,384; French Patent Publication No. 2653191; and the like.
In these prior art documents, the outer ring of the bearing is integrally formed with a sensor, but the outer ring of the bearing unit is connected to a knuckle-type support member extending from a chassis of an automobile to support the axle. This type of bearing unit has a double-row bell bearing because the axle to support the wheel is supported by the bearing unit only.
It should be noted that the support functions disclosed in FIG. 7, FIG. 8, No. H2-60802 and No. H2-83104 using a single-row ball bearing are quite different from those disclosed in the publications above using a double-row ball bearing. Specifically, in the former cases, the axle is supported at the opposite ends specifically at one end on the automobile wheel side by a single-row ball bearing with its outer ring connected to the axle tube or housing, and at the other end on the side of the differential gear box by another single-row ball bearing, while in the latter cases, the axle is supported only at one location by a double-row ball bearing.
In addition, the support type to which the bearing is applied is quits different between the bearing units in FIG. 7, FIG. 8, No. H2-60802 and No. H2-83104 using a single-row ball bearing and those in the publications above using a double-row ball bearing. Specifically, in the former cases, the bearing is mounted azid supported by the axle housing or tube containing oil therein, so that connecting means such as a mounting flange and sealing means for oil are required, while in the latter cases the bearing is mounted and supported by the knuckle-arm member, so that flange means connected to the axle housing or tube, and sealing means for oil in the axle housing or tube are not required.
Therefore, the bearing unit as mentioned in the publications using the double-row ball bearing could not be applied to a suspension system using the single-row bearing.
A structure for unitizing an axle-bearing, a sensor and a pulser ring for sensing rotational speed in a single-row roller bearing unit is disclosed in U.S. Pat. No. 4,940,936. In this U.S. patent, a single-row roller bearing is connected to an axle housing or tube, and has an outer ring through which a hole is provided to insert a sensor.
However, since the outer ring is presa-fitted into the axle tube the secured connection of the axle bearing unit with an axle tube is not sufficiently obtained while the axle bearing unit could not be easily disconnected from the axle tube for maintenance.
In addition, there is no seal means between the bearing and the axle tube, and between the axle tube and the outer ring, so that oil in the axle tube can be easily penetrate into the bearing and leak out of the arrangement.
Although the bearing unit of this U.S. patent has sensor inserted into a hole in the outer ring, it is still insufficient in reliability and maintenance operation.